I. Field of the Invention
The present invention relates generally to apparatus for providing signals indicative of the rotation position of a rotary shaft, such as the shaft on a flow control valve, and more particularly to an improved rotary shaft position indicating mechanism incorporating a visual display of the shaft position and an improved mounting arrangement affording greater flexibility in adapting the rotary shaft position indicating and display assembly in conjunction with other telemetry and control apparatus to a variety of devices in the field.
II. Discussion of the Prior Art
In the Wolford et al U.S. Pat. No. 4,214,133 there is disclosed a rotary shaft position switch used for telemetering the positioning of a rotatable shaft, such as on a flow control valve to a remote location for indicating whether that valve is opened or closed. The device of the aforereferenced patent, however, did not provide any means for visually indicating to persons within view of the valve assembly whether it is opened or closed.
Accord, Inc. of Cincinnati, Ohio, manufactures and sells a rotary shaft position indicator in which a cam shaft passes through the base portion thereof and is journaled for rotation therein. The cam shaft supports one or more cams for cooperating with Microswitches with the shaft passing upward through the housing cover and into a plastic dome having an inner member secured to the cam shaft and containing printed graphics information and an outer member which is generally opaque except for a transparent window through which the graphics information can be read.
The Accord device, therefore, required extra sealing to make the switch housing weather and water tight. Moreover, if it becomes necessary to remove the switch housing cover for adjustment of the cams relative to the switches, the cam shaft must also be slipped out of the seal to the visual indicator in the dome, thus making it necessary to reorient the display graphics upon reassembly. In addition, the size and positioning of the window through which the graphics can be observed is only viewable when the observer is positioned in a limited zone.
Another company, Proximity Controls, Inc., of Fergus Falls, Minn., manufactures and sells a line of valve position indicators also including a visual display capability. In the Proximity Controls, Inc.'s devices, the visual indicator is mounted to the switch enclosure at a location between the valve being monitored and the switches. The indicator in question is made of two plastic drums, one inside the other, where the inner drum includes words, symbols or other graphics which may be viewed through a window formed in the outer drum. While that arrangement is deemed to be an improvement over the Accord arrangement in that it does not require that the cam shaft pass through the switch housing cover into a display dome, it suffers from the drawback that the visual indicator is physically located beneath the switch housing such that it cannot be seen from above. Moreover, the window opening is relatively small in size, making the graphics information difficult to see from any appreciable distance.
The designs of the Accord and Proximity Controls rotary shaft position indicators have additional drawbacks, especially as it relates to adapting the devices to an existing valve or other mechanism with which it is to be used in the field. Specifically, when mounting the Proximity Controls device to an existing valve shaft, the screw holding the coupling yoke and the inner drum to the cam shaft must be loosened to set the inner drum to correspond to the window in the outer drum when the valve is in the OPEN or CLOSED position. Following that, the switch housing is then mounted. If the two drums do not correspond exactly, the switch housing must be removed, the yoke screw loosened to adjust the inner drum, then remounted. This may require several repetitions until proper alignment is achieved. When it becomes necessary to adjust the outer drum so as to move the window to a more visible location, it again becomes necessary to remove the housing to reposition the outer drum. Typically, new screw holes must be formed and following that, the unit must be reassembled with the inner drum being adjusted with the yoke attaching screw to again cause the graphics image to be viewable through the window of the outer drum when the rotary shaft is in the appropriate position indicated by the word visible through the window.
Still another problem with the prior art rotary shaft position indicators relates to the difficulty in adapting the indicator to the variety of valve types found in the field with which the indicators are to be used. Since there is no standard dimensions in terms of valve shaft length and lateral displacement of the mounting pad relative to the valve shaft location, suppliers of rotary shaft position indicators are forced to provide a wide variety of mountings to accommodate different manufacturers, size of valve and actuators as well as combinations of actuators and position indicators. Because of the hundreds of different valves and actuators to fit, attempts have been made by others to fabricate a universal bracket allowing a given model of shaft position indicator to fit many different valves and valve actuators but without much success.